In operating electric power tools, trigger switches are often used to enable an operator to manually turn on and off the power tools. The operator will grip a power tool with his hand around a handle, and his forefinger positioned on a trigger to selectively press and release it to operate the hand power tool. Such tools are portable in that they can be carried from place to place, either having their own power supply or being connectable to an electric power outlet to be ready for use. A person can manually grip the handle and be ready to perform the cutting or drilling work intended. Such portable power tools may be drills, saws, planers, etc. and other cutting means.
When using such portable power tools, accidents at times occur due to the cutting means of the power tool encountering unexpected hard objects. The reaction is such that the power tool is said at times to "kick-back" and then possibly injure the operator. A common reaction of the operator to such a kick-back reaction of the power tool is to "try harder" when a hard object worked on causes difficulty. Another reaction is to instinctively hold more tightly or grip harder, which is in the nature of a panic reaction. In any event, for these instances, the grip of the operator increases in intensity, which is often the cause of an accident.
Such accidents may be prevented if such an instinctive reaction of the operator to an unexpected power tool operation causes the shut-off of the electrical power tool.